The present invention relates to novel apparatus and an improved method for both stopping and restarting a tufting machine during its operation whereby the production of stop marks in the pile fabric may be substantially eliminated.
As is well-known in the carpet industry, a defect which often occurs during the production of tufted carpet when tufting machines are stopped or restarted is known as a stop mark or tufting streak. Stop marks are visible defects which appear on the face or pile side of a tufted carpet and generally extend across the entire width thereof. Normally, the tuft loops forming the face or pile side of the carpet have a predetermined pile height, with the pile height in plush type carpets being uniform while the pile height in sculptured carpets usually varies between two different pile heights. A stop mark, however, results when the row or rows of tuft loops closest the needles has some of the yarn pulled therefrom so that the height of the yarn therein is other than what it should be.
Over the years stop marks have been found to have resulted from a variety of causes. For example, as indicated in U.S. Pat. No. 3,762,346, if the yarn used in tufting carpets is held under tension for a long enough period while the machine is stopped, stop marks can result.
While operators normally attempt to stop tufting machines such that the needles are in their fully raised position above the backing fabric, holding the needles in such a position causes tension to be placed on the pile yarn since the thread jerk mechanism is exerting maximum tension on the yarn when the needles are raised. As suggested in this patent, prolonged tension sometimes causes elongation of the yarns and eventually a drawing out of the loops previously formed thereby producing a line of tufting loops across the face of the carpet which have a reduced pile height known as a stop mark which is quite clearly visible. In the above patent it was suggested that stop marks attributable to yarn tension could be eliminated by providing a yarn tension control mechanism so that when the needle bar was stopped tension commonly applied to the yarn was relaxed so that the tufting machine could be stopped for relatively long periods of time without causing elongation of the yarn.
Another attempt at overcoming stop mark problems is disclosed in U.S. Pat. No. 3,548,766. In this device, when the tufting machine was stopped, one set of rolls used to feed yarn to the tufting machine was continuously rotated in its yarn feed direction by an auxiliary drive but the roll pressure on the yarn was relaxed so that rather than be applying a full driving force the rolls were allowed to slip on the yarn. Thus, without actually continuing to feed yarns, the yarns were maintained under a positive tension and a retraction of the yarn from the puller rolls in a direction counter to that of the feed direction was prevented. In this way, the yarn was prevented from being pulled from the last row of tufted loops with the hope that stop marks would be prevented when the machine again began the tufting process.
Two other attempts to effectively eliminate stop marks dealt with the feeding of backing fabric through the tufting machine. In U.S. Pat. Nos. 2,840,019 and 2,857,867 the backing fabric was tensioned within predetermined limits and worm gears were used to effectively lock the backing fabric drive train so as to prevent any reverse movement of the backing fabric through the machine upon a start-up after the tufting machine had once been stopped. In effect, an attempt was made to limit the amount of backlash in the gear train feeding the backing fabric. As brought out in 2,840,019, the use of a slip clutch functions, in effect, to apply a sufficient positive load to the feed roll shafts which aided in eliminating the backlash in the backing fabric gear train and at the same time maintained a light tension on the fabric in the area between the feed rolls and the needle bar.